U.S. patent application number 11/515029 was filed with the patent office on 2007-12-06 for heat exchanger for fuel cell.
This patent application is currently assigned to Samsung SDI Co., Ltd.. Invention is credited to Seung-jae Lee, Tae-won Song.
Application Number | 20070277960 11/515029 |
Document ID | / |
Family ID | 38503953 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070277960 |
Kind Code |
A1 |
Song; Tae-won ; et
al. |
December 6, 2007 |
Heat exchanger for fuel cell
Abstract
A heat exchanger that can mechanically automatically control a
level of cooling water according to heat generation of the fuel
cell. The heat exchanger includes a housing having a cooling water
inlet and an outlet connected to a fuel cell stack, a moving plate
which moves reciprocally in the housing and discharges cooling
water filled in the housing to the stack when it moves in a one
direction and when it receives a steam pressure from the stack it
moves in an opposite direction, and an elastic member that applies
a force to the moving plate in the one direction. The heat
exchanger can automatically maintain the level of cooling water
despite a difference in heat generated between a full and a partial
load operation of the fuel cell obviating complicated electronics
such as a thermo-sensor, a valve, or a controller. Also, under a
partial load, the exposure of flow channels to superheated steam is
avoided, thereby extending the lifetime of the fuel cell.
Inventors: |
Song; Tae-won; (Seoul,
KR) ; Lee; Seung-jae; (Seongnam-si, KR) |
Correspondence
Address: |
STEIN, MCEWEN & BUI, LLP
1400 EYE STREET, NW, SUITE 300
WASHINGTON
DC
20005
US
|
Assignee: |
Samsung SDI Co., Ltd.
Suwon-si
KR
|
Family ID: |
38503953 |
Appl. No.: |
11/515029 |
Filed: |
September 5, 2006 |
Current U.S.
Class: |
165/86 ; 165/163;
429/437; 429/452 |
Current CPC
Class: |
F28D 15/06 20130101;
Y02E 60/50 20130101; F28D 2021/0043 20130101; H01M 8/04029
20130101; F28F 2265/14 20130101; F28D 15/0266 20130101; F28D 7/024
20130101 |
Class at
Publication: |
165/86 ; 429/26;
165/163 |
International
Class: |
F28D 7/02 20060101
F28D007/02; H01M 8/04 20060101 H01M008/04; F28D 11/00 20060101
F28D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2006 |
KR |
2006-49997 |
Claims
1. A heat exchanger for a fuel cell, comprising: a housing having a
cooling water inlet and a cooling water outlet connected to a stack
of the fuel cell; a moving plate which moves reciprocally in the
housing and discharges cooling water filled in the housing to the
stack through the cooling water outlet when the moving plate moves
in one direction and receives a pressure of steam entering through
the cooling water inlet when the moving plate moves in an opposite
direction; and an elastic member that applies an elastic force in
the one direction to the moving plate.
2. The heat exchanger of claim 1, further comprising a separation
element that separates an upper space of the moving plate where the
steam pressure is applied from a lower space of the moving plate
where the elastic force of the elastic member is applied to prevent
the flow of cooling water between the upper space and the lower
space.
3. The heat exchanger of claim 1, wherein the separation element
comprises an O-ring that is inserted into a rim portion of the
moving plate and seals a gap between the moving plate and an inner
wall of the housing.
4. The heat exchanger of claim 1, wherein the separation element
comprises a diaphragm that covers the space under the moving plate
where the elastic force is applied.
5. The heat exchanger of claim 1, wherein the separation element is
a bellows tube that surrounds the elastic member.
6. The heat exchanger of claim 1, wherein the housing comprises a
flow channel for passing secondary cooling water for exchanging
heat with the cooling water that circulates in the stack.
7. The heat exchanger of claim 6, wherein a wall of the housing
comprises a flow channel for passing secondary cooling water for
exchanging heat with the cooling water that circulates in the
stack.
8. The heat exchanger of claim 1, wherein an air hole is formed in
the housing in an area where the elastic member is disposed so that
air freely flows in and out of the housing area where the elastic
member is disposed.
9. The heat exchanger of claim 1, wherein the housing and the
moving plate are formed of one material selected from the group
consisting of stainless steel, rubber, and polymer.
10. The heat exchanger of claim 1, wherein the elastic member
comprises a first spring that applies an elastic force to the
moving plate in an entire moving distance in the one direction and
a second spring that applies an elastic force to the moving plate
when the moving plate moves by a predetermined distance in the
opposite direction.
11. The heat exchanger of claim 1, wherein the elastic member
comprises an adjustment member to increase or decrease the elastic
force.
12. A heat exchanger for a fuel cell, comprising: a housing
comprising: a cooling water inlet and a cooling water outlet
connected to a stack of the fuel cell, an elastic bellows in a
lower portion of the housing, and a moving plate which moves
reciprocally at an end of the bellows and discharges cooling water
filled in the housing to the stack through the cooling water outlet
when the moving plate moves in one direction and receives a
pressure of steam entering through the cooling water inlet when the
moving plate moves in an opposite direction.
13. The heat exchanger of claim 12, wherein a wall of the housing
comprises a flow channel for passing secondary cooling water for
exchanging heat with the cooling water that circulates in the
stack.
14. A heat exchanger for a fuel cell, comprising: a first housing
having a cooling water inlet and a cooling water outlet connected
to a stack of the fuel cell; a second housing hydraulically
connected to the first housing; a moving plate which moves
reciprocally in the second housing and discharges cooling water
filled in the first and second housings to the stack through the
cooling water outlet when the moving plate moves in one direction
and receives a pressure of steam entering through the cooling water
inlet when the moving plate moves in an opposite direction; and an
elastic member that applies an elastic force in the one direction
to the moving plate.
15. A heat exchanger for a fuel cell, comprising: a housing having
a cooling water inlet and a cooling water outlet connected to a
stack of the fuel cell; a moving plate to automatically control a
level of water in the housing; an elastic member to exert a force
on the moving plate, wherein the moving plate is in equilibrium
between a steam pressure from the cooling water inlet and the
elastic member.
16. The heat exchanger of claim 15, wherein the plate moves a
distance .DELTA.X between a full load operation and a partial load
operation of the fuel cell according to the equation,
.DELTA.F=k.DELTA.X=A(P.sub.h-P.sub.atm) where F is a working force,
k is a coefficient of elasticity of the elastic member, A is an
area of the moving plate, P.sub.h is a steam pressure, and
P.sub.atm is the atmospheric pressure.
17. The heat exchanger of claim 15, wherein the elastic member is
non-linear to exert an automatic control of the water level when
heat generated fluctuates between a full load operation and a
partial load operation of the fuel cell, and to prevent a rapid
change of position of the moving plate according to the increase in
the steam pressure, thereby ensuring a stable control.
18. The heat exchanger of claim 17, wherein the elastic member
comprises: a first spring to exert the force on the moving plate
over an entire range of motion of the moving plate; and a second
spring to exert a force on the moving plate only over a portion of
the range of motion of the moving plate.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims the benefit of Korean Application
No. 2006-49997, filed Jun. 2, 2006, in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Aspects of the present invention relate to a heat exchanger
for a fuel cell, and more particularly, to a heat exchanger that
can automatically control the level of cooling water according to
the heat generation of a fuel cell.
[0004] 2. Description of the Related Art
[0005] A fuel cell is an apparatus that transforms chemical energy
of a fuel directly into electrical energy through a chemical
reaction. Thus, the fuel cell is a kind of electric generator that
can generate electricity as long as a fuel is supplied.
[0006] FIG. 1 is a schematic drawing showing the principle of
generating electricity from a conventional fuel cell. Referring to
FIG. 1, electricity is generated by a reverse reaction of the
electrolysis of water taking place through an electrolyte membrane
2 when air, which contains oxygen, is supplied to a cathode 1 and a
fuel containing hydrogen is supplied to an anode 3. However, a
voltage of the electricity generated from a unit cell 4 is not
usually high enough to be used. Therefore, as depicted in FIG. 2, a
plurality of unit cells 4 is connected in series in a stack 10.
[0007] During the electrochemical reaction, not only electricity
but also heat is generated. Therefore, to maintain a smooth
operation of the fuel cell, the heat must be continuously
dissipated. Accordingly, a heat exchanger 20, as depicted in FIG.
2, is provided in the fuel cell. Referring to FIG. 2, flow channels
4a for passing cooling water for exchanging heat are formed in each
unit cell 4 of the fuel cell. The cooling water absorbs heat from
the stack 10 while passing through the flow channels 4a. The
cooling water that absorbs the heat is cooled down by secondary
cooling water in the heat exchanger 20, and is re-circulated
through the flow channels 4a of the stack 10. At this time, the
circulation of the cooling water is not achieved by an additional
force, but by natural convection of water, that is, by overflow of
boiling water due to the heat absorbed from the surroundings. For
example, as depicted in FIG. 3, when the cooling water is filled in
the flow channels 4a at an appropriate level, the cooling water
starts absorbing heat, and as a result, the cooling water starts
boiling and overflows. The cooling water that overflows enters the
heat exchanger 20 and is cooled down by secondary cooling water.
Afterward, the cooled cooling water is re-circulated in the stack
10.
[0008] However, in many cases, the fuel cell is operated at a load
smaller than a designed load. This is called a partial load
operation state wherein the fuel cell generates less power than the
designed power. In this state, the amount of heat generated is
reduced, and thus, the amount of heat absorbed by the cooling water
is also reduced. Thus, the convection of the cooling water is not
achieved properly since the cooling water does not boil enough to
overflow. In the related art, to solve this problem, the
temperature of the cooling water entering the heat exchanger 20 is
measured using a thermo-sensor 30. If the temperature of the
cooling water is lower than a designed value, that is, the fuel
cell operates in a partial load operation state, the cooling
operation is not performed until the temperature of the cooling
water in the stack 10 rises enough so that the cooling water can be
circulated by closing a solenoid valve 40 installed at a cooling
water outlet of the heat exchanger 20.
[0009] However, in this method, the cooling water does not overflow
but fluctuates, that is, the water level in the stack 10 goes up
and down until the temperature of the cooling water rises enough to
be circulated. Thus, some regions of the flow channels 4a do not
come in to contact with the cooling water for a period of time. As
a result, these regions are exposed to superheated steam for a
period of time, and thus the thermal resistance of the stack 10 is
greatly reduced.
[0010] Also, this system requires complicated control devices such
as the thermo-sensor 30 for measuring the temperature, the solenoid
valve 40 for closing and opening the flow channels 4a, and a
controller (not shown) for controlling these elements.
SUMMARY OF THE INVENTION
[0011] Aspects of the present invention provide a heat exchanger
for a fuel cell, the heat exchanger having a simple structure that
can ensure thermal safety in a stack of the fuel cell in a partial
load operation state.
[0012] According to an aspect of the present invention, there is
provided a heat exchanger for a fuel cell, comprising: a housing
having a cooling water inlet and a cooling water outlet connected
to a stack of the fuel cell; a moving plate which moves
reciprocally in the housing and discharges cooling water filled in
the housing to the stack through the cooling water outlet when it
moves in one direction and receives a pressure of steam entering
through the cooling water inlet when it moves in an opposite
direction; and an elastic member that applies an elastic force in
the one direction to the moving plate.
[0013] While not required in all aspects, the heat exchanger may
further comprise a separation element that separates an upper space
of the moving plate where the steam pressure is applied from a
lower space of the moving plate where an elastic force of the
elastic member is applied to prevent the flow of cooling water
between the upper space and lower space.
[0014] While not required in all aspects, the separation element
may comprise an O-ring that is inserted into a rim portion of the
moving plate to seal a gap between the moving plate and an inner
wall of the housing, and one of a diaphragm that covers the space
under the moving plate where the elastic force is applied or a
bellows tube that surrounds the elastic member.
[0015] While not required in all aspects, the housing may comprise
a flow channel for passing secondary cooling water for exchanging
heat with the cooling water that circulates in the stack, and an
air hole may be formed in the housing in an area where the elastic
member is disposed so that air acts in the housing.
[0016] While not required in all aspects, the housing and the
moving plate may be formed of one material selected from the group
consisting of stainless steel, rubber, and polymer.
[0017] While not required in all aspects, the elastic member may
comprise a first spring that applies an elastic force to the moving
plate along the entire moving distance in the one direction and a
second spring that applies an elastic force to the moving plate
when the moving plate moves down by a predetermined distance in the
opposite direction.
[0018] Additional aspects and/or advantages of the invention will
be set forth in part in the description which follows and, in part,
will be obvious from the description, or may be learned by practice
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and/or other aspects and advantages of the invention
will become apparent and more readily appreciated from the
following description of the embodiments, taken in conjunction with
the accompanying drawings of which:
[0020] FIG. 1 is a schematic drawing showing the principle of
generating electricity of a conventional fuel cell;
[0021] FIG. 2 is a perspective view of a structure of a fuel cell
having a conventional heat exchanger;
[0022] FIG. 3 is a partial perspective view of a flow channel in a
stack of the fuel cell of FIG. 2;
[0023] FIG. 4 is a cutaway perspective view of a fuel cell having a
heat exchanger according to an embodiment of the present
invention;
[0024] FIGS. 5A and 5B are cross-sectional views for respectively
illustrating a full load operation and a partial load operation of
the heat exchanger of FIG. 4;
[0025] FIG. 6 is a cross-sectional view of a heat exchanger
according to another embodiment of the present invention;
[0026] FIGS. 7 and 8 are partial perspective views of a modified
version of the fuel cell heat exchanger of FIG. 4;
[0027] FIGS. 9A and 9B are cross-sectional views for respectively
illustrating a full load operation and a partial load operation of
the heat exchanger according to another embodiment of the present
invention; and
[0028] FIG. 10 is a cross-sectional view for illustrating a heat
exchanger according to another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0029] Reference will now be made in detail to the present
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings, wherein like reference
numerals refer to the like elements throughout. The embodiments are
described below in order to explain the present invention by
referring to the figures.
[0030] FIG. 4 is a cutaway perspective view of a fuel cell having a
heat exchanger 100 according to an embodiment of the present
invention.
[0031] Referring to FIG. 4, the heat exchanger 100 includes a
housing 110 having an inlet 111 and an outlet 112 for cooling water
circulating along flow channels 4a formed in a stack 10, a moving
plate 120 which moves reciprocally in the housing 110, and a spring
130 which is an elastic member and applies an elastic force to the
moving plate 120 to make it move upward.
[0032] The moving plate 120 serves as a bottom surface of an inner
space of the housing 110, where cooling water entering through the
inlet 111 is filled. An upper surface of the moving plate 120
receives a pressure of steam entering from the stack 10, and a
lower surface of the moving plate 120 receives an elastic force of
the spring 130 together with atmospheric pressure through an air
hole 113. Accordingly, the moving plate 120 stops at a position
where an equilibrium state is achieved between the steam pressure
on the upper surface and the elastic force acting on the lower
surface. Reference numeral 140 denotes an O-ring, which is an
element for separating the upper and lower spaces of the moving
plate 120 and seals a gap between the moving plate 120 and an inner
wall of the housing 110. Although the description of the embodiment
is made with reference to upper and lower, the present invention is
not limited to such a vertical orientation. For example, the moving
plate 120, elastic spring 130 and O-ring 140 can be arranged on one
side of the housing 110 or otherwise hydraulically connected to the
housing 110.
[0033] When the fuel cell having the heat exchanger 100 for cooling
operates in a full load state, convection of the cooling water is
smoothly achieved since heat is actively generated in the stack 10
and steam pressure in the housing 110 increases. Therefore, as
depicted in FIG. 5A, the moving plate 120 is in an equilibrium
state where the spring 130 is slightly compressed. Thus, the
cooling water circulates through the flow channels 4a between the
housing 110 and the stack 10, and heat exchange takes place between
the cooling water and secondary cooling water that circulates
through a coil shaped flow channel 150. While not required in all
aspects, the flow channel 150 may be in the wall of the
housing.
[0034] However, when heat generation in the stack 10 is reduced due
to a partial load operation, the steam pressure acting in the
housing 110 is also reduced. In this state, the steam pressure that
presses on the moving plate 120 is relatively reduced, and thus, as
depicted in FIG. 5B, the moving plate 120 moves up. Accordingly, a
height of the cooling water, that is, the height from the moving
plate 120 which is a bottom surface to the outlet 112 is reduced.
As a result, a larger amount of cooling water flows into the flow
channels 4a of the stack 10. Accordingly, the water level of the
cooling water filled in each of the cells in the stack 10 rises.
Therefore, the cooling water can easily boil and overflow even when
a small amount of heat is generated in the stack 10, and thus the
cooling water can flow into the housing 110 of the heat exchanger
100. In this way, if the circulation of the cooling water is
smooth, no region of the flow channels 4a is exposed to superheated
steam, thereby ensuring the safety of the stack 10.
[0035] In other words, the heat exchanger 100 according to an
aspect of the present invention does not control the circulation of
cooling water by controlling closing or opening of a valve using a
controller after measuring the temperature of the cooling water
like in the related art, but the water level in the housing 110 is
automatically controlled while a mechanical equilibrium between the
steam pressure and the spring 130 is maintained. Accordingly,
differences in heat generated in a full load operation and a
partial load operation can be automatically controlled without
using complicated electronic apparatuses such as a thermo-sensor
30, a valve, and a controller like in the prior art.
[0036] According to an embodiment of the present invention, the
housing 110 may include an elastic bellows 115 in a lower portion
as shown in FIGS. 9A and 9B. In such an embodiment the O-ring 140,
spring 130, and air holes 113 may not be required. The operation of
the fuel cell having the heat exchanger 100'' with a lower bellows
operates the same as that described above in reference to FIG. 5A
and FIG. 5B in a full load and partial load states, respectively,
with the bellows supplying the elastic force.
[0037] A moving distance .DELTA.X of the moving plate 120 between a
full load operation and a partial load operation can be calculated
using the following equation.
.DELTA.F=k.DELTA.X=A(P.sub.h-P.sub.atm)
where F is a working force, k is a coefficient of elasticity of the
spring 130, A is an area of the moving plate 120, P.sub.h is a
steam pressure, and P.sub.atm is the atmospheric pressure.
[0038] The housing 110 and the moving plate 120 may be formed of a
material having high thermal resistance such as stainless steel,
rubber, or polymer. An adjustment member 114 may be connected to
the spring 130 to increase or decrease the tension in the spring
130 as shown in FIG. 10.
[0039] FIG. 6 is a cross-sectional view of a heat exchanger 100'
according to another embodiment of the present invention. The same
reference numerals are used to indicate elements identical with
those depicted in FIGS. 4 through 5B.
[0040] The heat exchanger 100' according to the present embodiment
has the same basic structure as the heat exchanger 100, that is,
the water level is controlled by the equilibrium between a steam
pressure and an elastic force of an elastic member respectively
acting on both sides of the moving plate 120. However, the elastic
member in FIG. 6 has a double structure in which first and second
springs 131 and 132 are combined unlike in the previous embodiment.
That is, the first spring 131 provides an elastic force to the
moving plate 120 in the entire moving region like in the previous
embodiment. The second spring 132 is installed to provide an
elastic force to the moving plate 120 when the moving plate 120
moves down by a certain distance, that is, when the moving plate
120 is lowered by a predetermined distance by the increase in the
steam pressure. This is because the increase in the steam pressure
in the housing 110 according to the increase in the heat generation
in the stack 10 is not linear but follows a parabolic curve. In
this case, the elastic force of the second spring 132 is added to
the first spring 131 when the steam pressure increases rapidly in
response to the increase in the heat generation in the stack 10.
Therefore, a rapid change of position of the moving plate 120
according to the increase in the steam pressure can be avoided. The
rest of the configuration and the principle of operation are the
same as in the previous embodiment, and thus, the description
thereof will not be repeated.
[0041] The use of the heat exchanger 100' according to aspects of
the present invention allows an automatic control of the water
level in the case of a difference in heat generated between a full
load operation and a partial load operation, and also prevents a
rapid change of position of the moving plate 120 according to the
increase in the steam pressure, thereby further ensuring a stable
control.
[0042] In the above embodiments, the O-ring 140 is used as an
element for separating the steam pressure region from the elastic
force region, but the present invention is not limited thereto.
That is, instead of the O-ring 140, a diaphragm 141 as depicted in
FIG. 7 or a bellows tube 142 as depicted in FIG. 8 can also be
used.
[0043] The heat exchanger, according to aspects of the present
invention, has the following advantages. First, variations in the
water level caused by a difference in heat generated between a full
load operation and a partial load operation can be controlled
without using complicated electronic apparatuses such as a
thermo-sensor, a valve, or a controller as in the related art.
Second, when the fuel cell operates in a partial load state, the
exposure of regions of flow channels to superheated steam can be
avoided, thereby extending the lifetime of the fuel cell.
[0044] Although a few embodiments of the present invention have
been shown and described, it would be appreciated by those skilled
in the art that changes may be made in this embodiment without
departing from the principles and spirit of the invention, the
scope of which is defined in the claims and their equivalents.
* * * * *